Stanford probably has the strongest program in evironmental science. 8 Stanford faculty members in environmental science belong to the prestigious National Academy of sciences (NAS), while Harvard has 0 in NAS. You can search that through the link below
National Academy of Sciences:.
In addition to that, Stanford's evironmental engineering program has been #1 for decades by US News graduate school rankings. See the rankings:
1 Stanford University Stanford, CA 4.6
2 University of California--Berkeley Berkeley, CA 4.5
3 University of Illinois--Urbana-Champaign Urbana, IL 4.3
4 University of Texas--Austin (Cockrell) Austin, TX 4.2
5 University of Michigan--Ann Arbor Ann Arbor, MI 4.1
6 Georgia Institute of Technology Atlanta, GA 4.0
Johns Hopkins University (Whiting) Baltimore, MD 4.0
8 California Institute of Technology Pasadena, CA 3.9
Carnegie Mellon University Pittsburgh, PA 3.9
10 Massachusetts Institute of Technology Cambridge, MA 3.8
University of North Carolina--Chapel Hill Chapel Hill, NC 3.8
Virginia Tech Blacksburg, VA 3.8
Environmental/Environmental Health - Engineering - Best Graduate Schools - Education - US News and World Report